A great number of writers (some of whom really ought to know better) don’t seem to realize SEAL is an acronym; it stands for Sea, Air and Land.
A Navy SEAL team is suddenly transported through time to an age of steel and sword. Lacking other useful skills for this age, they become assassins in order to make a living.
Assuming this story idea is meant to be about time travel rather than an alternate-universe thing, I should point out that there was far less work for professional assassins in the “age of steel and sword” (whatever the hell that means — I’m guessing the writer meant the Middle Ages or earlier) than you might think. Also, anyone with that much military training/experience could also work as a security guard for nobles or wealthy merchants, actually join the military in the place they find themself, etc. Plus, what about all the other skills that a person from the modern world should have that could give them an advantage — or at least a way to make a decent living — in a less technologically advanced era? The basic premise of “send some highly trained military personnel from the modern era back in time several hundred years” is sound — a lot of good stories have been written using variations on the theme — but the details need more thought.